1. Field of the Invention
The present invention relates to photopolymerizable compositions, and particularly, to photopolymerizable compositions containing a post-exposure polymerization inhibitor.
2. Description of the Prior Art
It is known that images can be formed by a process which comprises: (1) producing a photosensitive material having a layer including a photopolymerizable composition (the sensitive layer) by applying a solution of a photopolymerizable composition comprising an addition-polymerizable compound having at least one ethylenically unsaturated double bond (the ethylenic compound), a photopolymerization initiator and, if desired, a film forming high molecular weight substance (the binder), a thermal polymerization inhibitor, a plasticizer, etc., to a first base; (2) imagewise exposing the sensitive layer to light with using a desired original, to thereby harden the exposed parts of the sensitive layer by polymerization; and (3) removing the unexposed unhardened parts of the sensitive layer by dissolution. This process is referred to as solvent development. An alternative process comprises: (1) bonding the sensitive layer of the photosensitive material as described above to an image-receiving base (with either the first base of the photosensitive material or the image-receiving base being transparent) to produce a laminate; (2) imagewise exposing the laminate to light through the transparent base to polymerize the exposed part of the sensitive layer, as a result of which the relative adhesive strength of the sensitive material to the first base and that to the image-receiving base varies between the exposed part and the unexposed part, such that upon separating the bases from each other by stripping the unexposed part of the sensitive layer adheres to the opposite base (to the base adhered to by the exposed layer) to form an image of the sensitive layer. This process is referred to as stripping development.
In these processes, there is no problem in case of forming images by solvent development or stripping development if the development is conducted shortly after imagewise exposure. However, if the development is carried out after a substantial lapse of time from the time of the exposure, radicals formed by the exposure remain even after the exposure, and therefore the polymerization reaction continues even after the exposure. Consequently, a phenomenon akin to excessive exposure occurs, causing faults upon image formation, such as collapse of letters, formation of thick lines, etc.
As a method of overcoming such a phenomenon, it has been proposed to add thermal polymerization inhibitors in order to capture the radicals. However, known thermal polymerization inhibitors such as phenols, aromatic amines, copper stearate, copper naphthol, mercaptan, dialkyl sulfides, phenothiazine, alkyl triphenyl phosphates or alkyl xanthates, etc., generally causes a large desensitization of the photopolymerized material exposed to light. Further, they are not effective for preventing post-exposure polymerization.